1CREATE TABLE my_table (
 2    my_number integer not null primary key
 3)
 4CREATE GENERATOR my_generator
 5CREATE TRIGGER my_before_trigger FOR my_table
 6    BEFORE INSERT
 7    AS
 8    BEGIN
 9    IF (NEW.my_number IS NULL)
10        THEN NEW.my_number = GEN_ID(my_generator, 1);
11    END